But KC-KC-Vampire-Vampire-Vampire shuts down all opponents and gets you infinite VPs. I think that needs a fix.
You either need a Torturer-like clause to opt not to discard or a Militia-like clause for players with more than X cards in hand.
I see the KC-KC-(...) set-up mentioned a ton. Is this a common issue in the custom card realm? This doesn't seem stronger than KC-KC-Bridge*3. Or KC-KC-Goons*3. KC is a strong card that enables strong plays, but should God-hands temper the design of lesser cards that much?
The issue here is the potential to shut down your opponents' turns. If you can get to the point of KC-KC-Bridge-Bridge-Bridge, you're in a position where you will almost certainly win and win big, but what it
doesn't do is obliterate any chance that your opponents will be able to respond. They'll still have a proper turn afterward (if you don't end the game that very turn). With the official Dominion cards, the only way you can lock out your opponents is by using King's Courts, Masquerade, and a discarder attack (Militia or Goons, for example) in conjunction. Note, however, that this combo was not noticed during playtesting of the game, and Donald X. has stated that he probably would have killed the combo if it had been noticed before publication.
(Though more recently he said maybe not, so who knows.)Thing is, though, you don't have to work as hard as that to lock your opponents out with this card. Double Throne Room, double Vampire will leave your opponents with a single card apiece. Worse still, imagine a 4-6 player game wherein every plays a single copy on their turn. Whoever goes last has no cards, or next to no cards, to play with. Contrast with any other attack in Dominion, be it Militia, Goons, Witch, Mountebank, or whatever. That last player will still get a decent shot at a turn, every time.
In some cases, the design of the official attack cards prevent lock-out in a very subtle way. Notice how Sea Hag doesn't just say "put a Curse on top of your deck." If it did, five plays would mean five Curses constituting the entirety of your next turn. Instead, the "discard the top card of your deck" bit ensures is a safeguard against lock-out.
Similarly, Rabble works on the top 3 cards instead of the top 5, and Torturer lets you take Curses instead of sacrificing your whole next turn to multiple Torturers played in a row.
Without safeguards against lock-outs like this, it would be too easy to build an engine that would shut your opponent(s) out for whole turns or even, indeed, the entire rest of the game, which doesn't wind up being a whole lot of fun for the victims and possibly not the attackers, either. True, it's not gamebreaking in the sense that there is something inherently wrong with the mechanics of a game that allowed lock-out, but it runs contrary to the principles upon which the official Dominion cards are founded. As such, fan cards that break those principles probably aren't going to go over well with the players who are attracted to Dominion in the first place because like like those very qualities.
And I like to point out, that it scales differently in multiplayer. I don't know if this intended, but in 4 player games, this can be pretty strong.
I tried to make it balanced for a 4-player game, which is why I decided against extra benefits.
Here, the issue is more that the potential point swing in a 2-player game is 1 VP per play, while in 4-player it's 3 VP per play. So triple the power. No fixed extra benefit (like a flat +$2 to the player) will either fix or further break this scaling issue.
Admittedly, some of the official Dominion attack cards do scale differently. Thief can get you 3 Golds in a 4-player game, but only 1 in a 2-player game. The likelihood that Thief will miss mitigates this difference somewhat, but the potential is still there. However, Thief is weak enough anyway that it's not massively overpowered at 4-player, just better.
Even with that category of cards, though, there are subtle scaling fixes. Pirate Ship is a great example. You don't get a coin on your mat for EVERY Treasure card you trash -- you only get a coin IF you trashed any Treasure cards. This is one way to rein in the scaling on your card: gain a VP if ANYBODY discards a Victory card. This has a drawback too: it'll mean players will have to be careful to respond to the attack in order (because in the last seat I'm going to wait to see if someone else discards a Victory card before discarding mine), thereby slowing down the game, so there are still issues to either try to fix or decide to live with. But it's one way in which the scalability issue might be addressed.
By the way, the posts in "The Bible of Donald X." subforum are also really interesting reads. They're all Donald X. telling stories about how Dominion was designed. There is mention somewhere, though I can't remember exactly, that he experimented with a "everybody discards a card" attack, ultimately realizing that the lock-out possibilities that introduced didn't lead to the kind of game he wanted to make. It's entertaining and illuminating stuff.
Anyway, a quick footnote: I do appreciate your interest in making simple cards. I agree that fan cards tend to be more complex than they need to be, and I'm a huge fan of very simple cards that nevertheless allow for interesting strategy.
